Styrenic block copolymers (SBCs), most notably those of DuPont's Kraton® family, such as styrene-butadiene type polymers (e.g., styrene-butadiene di-block, SB; styrene-butadiene-styrene tri-block, SBS), have historically served the asphalt and footwear industries for years, with markets also in the industries of packaging, pressure sensitive adhesives, packaging materials, etc. Of these markets, the use of SBSs as bitumen modifiers is one of the largest and the most forgiving in terms of material properties.
The global asphalt market is to reach 118.4 million metric tons by 2015, according to a January 2011 report by Global Industry Analysts, Inc. The asphalt paving industry accounts for the largest end-use market segment of asphalt. With increasing growth in the developing markets of China, India, and Eastern Europe, asphalt will be increasingly needed to construct roadway infrastructure for the next decade. The increased demand for asphalt, along with the need for improved asphalt materials/pavement performance, creates the opportunity for an asphalt modifier.
The grade of the asphalt governs the performance of paving mixtures at in-service temperatures. In many cases, the characteristics of bitumen needs to be altered to improve its elastic recovery/ductility at low temperatures for sufficient cracking resistance as well as to increase its shearing resistance for sustained loads and/or at high temperatures for rutting resistance. The physical properties of bitumen are typically modified with the addition of SBS polymers to produce an improved asphalt grade that enhances the performance of asphalt paving mixtures. Of the asphalt mixtures that are polymer modified, approximately 80% of polymer modified asphalt uses SBS-type polymers.
Over the past few years, the price of butadiene, the principal component of SBC polymers used for bitumen modification, has increased dramatically. In 2008, there was a shortage of SBS polymers for the asphalt industry. With the forecast of increasing demand of liquid asphalt for the next decade, there remains a strong need for a new type of cost-effective, environment-friendly, viable polymers that can be used as an asphalt modifier in lieu of standard styrene-butadiene type modifiers.
Vegetable oils have been considered as monomeric feedstocks for the plastics industry for over 20 years. Polymers from vegetable oils have obtained increasing attention as public policy makers and corporations alike have been interested in replacing traditional petrochemical feedstocks due to their environmental and economic impact.
To date, moderate success has been achieved through the application of traditional cationic and free radical polymerization routes to vegetable oils to yield thermoset plastics (i.e., plastics which, once synthesized, permanently retain their shape and are not subject to further processing). For example, a variety of polymers, ranging from soft rubbers to hard, tough plastics were made by using cationic copolymerization of vegetable oils, mainly soybean oil (SBO), using boron triflouridediethyletherate (BFE) as initiator (Andjelkovic et al., “Novel Polymeric Materials from Soybean Oils: Synthesis, Properties, and Potential Applications,” ACS Symposium Series, 921: 67-81 (2006); Daniel & Larock, “Thermophysical properties of conjugated soybean oil/corn stover biocomposites.” Bioresource Technology 101(15):6200-06 (2010)). Soybean-oil-based waterborne polyurethane films were synthesized with different properties ranging from elastomeric polymers to rigid plastics by changing the polyol functionality and hard segment content of the polymers (Lu et al., “New Sheet Molding Compound Resins From Soybean Oil. I. Synthesis and Characterization,” Polymer 46(1):71-80 (2005); Lu et al., “Surfactant-Free Core-Shell Hybrid Latexes From Soybean Oil-Based Waterborne Polyurethanes and Poly(Styrene-Butyl Acrylate),” Progress in Organic Coatings 71(4):336-42 (2011)). Moreover, soybean oil was used to synthesize different bio-based products such as sheet molding composites, elastomers, coatings, foams, etc. (Zhu et al., “Nanoclay Reinforced Bio-Based Elastomers: Synthesis and Characterization,” Polymer 47(24):8106-15 (2006)). Bunker et al. (Bunker et al., “Miniemulsion Polymerization of Acrylated Methyl Oleate for Pressure Sensitive Adhesives,” International Journal of Adhesion and Adhesives 23(1):29-38 (2003); Bunker et al., “Synthesis and Characterization of Monomers and Polymers for Adhesives from Methyl Oleate,” Journal of Polymer Science Part A: Polymer Chemistry 40(4):451-58 (2002)) synthesized pressure sensitive adhesives using mini-emulsion polymerization of acrylatedmethyloleate, a monoglyceride derived from soy bean oil; the polymers produced were comparable to their petroleum counterparts. Zhu et al., “Nanoclay Reinforced Bio-Based Elastomers: Synthesis and Characterization,” Polymer 47(24):8106-15 (2006), generated an elastic network based on acrylated oleic methyl ester through bulk polymerization using ethylene glycol as the crosslinker, obtaining a high molecular weight linear polymer using mini-emulsion polymerization. Lu et al., “New Sheet Molding Compound Resins From Soybean Oil. I. Synthesis and Characterization,” Polymer 46(1):71-80 (2005), created thermosetting resins synthesized from soybean oil that can be used in sheet molding compound applications by introducing acid functionality onto the soybean and reacting the acid groups with divalent metallic oxides or hydroxides, forming the sheet. Bonnaillie et al., “Thermosetting Foam With a High Bio-Based Content From Acrylated Epoxidized Soybean Oil and Carbon Dioxide,” Journal of Applied Polymer Science 105(3):1042-52 (2007), created a thermosetting foam system using a pressurized carbon dioxide foaming process of acrylated epoxidized soybean oil (AESO). U.S. Pat. No. 6,121,398 to Khot et al., synthesized liquid molding resins that are able to cure into high modulus thermosetting polymers and composites using triglycerides derived from plant oils.
However, uncontrolled chain branching and crosslinking is inevitable by using these conventional polymerization routes due to the multifunctional nature of triglycerides, multiple initiation sites along the chain backbone, and chain transfer/termination reactions. While these thermoset materials may indeed supplant a number of petrochemically-derived thermosets, the vast majority of commodity polymers are highly processable thermoplastic materials. There is thus a need in the art to develop from vegetable oils a highly processable thermoplastic and elastomeric polymer with a wide range of applications and physical properties.
The present invention is directed to fulfilling these needs in the art.